In recent years, as an electro-photographic photoreceptor, organic electro-photographic photoreceptors (hereafter, referred to as organic photoreceptors or also merely referred to as photoreceptors) containing organic photoconductive materials are most widely used. As compared with other type photoreceptors, the organic photoreceptors have advantageous points, such as, it is easy to develop materials corresponding to various exposure light sources from visible light to infrared light, it is possible to select materials free from environmental pollution, and manufacturing cost is cheap. However, the organic photoreceptors have problems, such as, mechanical strength is weak, deterioration or blemish tend to take place on their surfaces at the time of copying or printing a number of sheets.
As an assignment for improving the durability of the organic photoreceptors, a structure to suppress abrasion due to scratch of a cleaning blade has been required strongly. As approach for such a structure, a technique to provide a protective layer with high strength on the surface of a photoreceptor has been studied. For example, as a surface layer of a photoreceptor, a technique to employ a colloidal silica-containing curable siloxane resin is reported (Patent Document 1). In the colloidal silica-containing curable siloxane resin, the curable resin with a siloxane bond (Si—O—Si bond) and also the colloidal silica have a high hygroscopic property. Therefore, the electric resistance of the surface layer falls easily, and image blurring and image flowing tend to take place.
Further, as a curable resin applied to a protective layer, a protective layer of a curable resin obtained by photo-polymerization with the use of a compound having an acryloyl group is proposed (Patent Document 2). In the protective layer, filler such as a metal oxide are contained in the curable resin. However, binding between the filler and the curable resin is weak, the intensity as a protective layer is insufficient, and problems such as image blurring and image flowing cannot be solved yet sufficiently.
Furthermore, it is reported that alumina particles of a trigonal system as filler contained in a protective layer are effective to improve image blurring (Patent Document 3). However, in this protective layer, binding between the alumina particles and a binder resin in the protective layer is weak, uniform dispersion of the alumina particles in the protective layer becomes insufficient, and the strength as the protective layer is weak. Accordingly, poor cleaning occurs. As a result, problems of image blurring cannot be solved sufficiently.
Moreover, if alumina particles sold on the commercial market are used for the alumina particles, deterioration of electric potential characteristics is observed together with image blurring when the photoreceptor is used repeatedly. As a result, such a phenomenon becomes an obstacle in the case of employing alumina particles as filler of a protective layer.
Patent Document 1: Japanese Unexamined Patent Publication No. 6-118681
Patent Document 2: Japanese Unexamined Patent Publication No. 2001-125297
Patent document 3: Japanese Unexamined Patent Publication No. 2003-98712